If you are using command line javac tool then this will be more problematic. Check parameters of javac command. You will need to place these classes correctly to your classpath or show the place of these classes as classpath to the javac!

If you are using an IDE like Netbeans, all you need to do is to select Properties of the Project and add the jar containing these classes or the directory containing these classes using a dialog.. And IDE will inform the compiler itself automatically.

From what you have posted, it is tough to tell where the problem would be. Is the main class in the same directory as the Decoder class? If it isn't, change your package statement at the top to import.

This might be a silly question, but have you checked your classpath? From looking at your code above, you're using some sort of IDE so it should be pretty easy to find. Just search the help docs for 'classpath.'